The attempt to determine the net global motion of components in an ensemble of dynamically moving scattering sites has proved to be complex, given that many ensembles of scattering sites possess two modes of motion: a global velocity component and a differential velocity component. It is the presence of the random motion that adds noise to the system and inhibits the optimum performance of the sensor. By suppressing this noise in an optical manner, less of the system's dynamic range need be sacrificed. Therefore, optimal use of the dynamic range of the detection apparatus and/or post-processing can be realized, thus the sensor performance is highly optimized.
In general, major concerns of such remote sensors include overall system efficiency, maintaining optical interrogation probe beams on the scattering sites under dynamic conditions, minimizing undesirable scattering, which can either corrupt the measurement or reveal the probing operation to an undesirable third part, and avoiding optical damage of the medium undergoing interrogation due to system inefficiency.
Currently, the prior art that exists in remote sensors involves complex adaptive optical compensation systems and light detection and ranging (lidar) approaches. These approaches require intensive post processing which makes them unattractive in many applications.
A conventional laser-ultrasonic non-destructive inspection system is taught Pepper et al. in U.S. Pat. No. 5,585,921 which issued on Dec. 17, 1996.
There are two system bandwidth parameters that characterize the performance of a sensing system: the detection bandwidth, also known as the coherent bandwidth, defined as the maximum global motion, or Doppler shift, that can be detected by the system, and the noise reduction bandwidth, also known as the incoherent bandwidth, defined as the maximum differential Doppler shift that can be suppressed by the system.